The present invention generally relates to data processors, and more particularly to a data processor which is useful for a single chip microcomputer, for example.
Generally, a processor portion is only integrated and formed on one semiconductor substrate in a general purpose multichip microprocessor. As described in pages 540 to 541 of "LSI HANDBOOK" published by OHM Corp. on Nov. 30th in 1984, a central processing unit, as a center part, a read only memory (ROM) for storing programs, a random access memory (RAM) for storing data and an I/O circuit for input and output of data and other functional blocks are formed on one semiconductor substrate. When a system is constituted by using the single chip microcomputer, the number of wires can be largely reduced as compared with the case where the system is constituted by using the general purpose multichip microprocessor. However, since an internal bus is also formed on the one common semiconductor substrate in the single chip microcomputer, the functional blocks are limited in use and it is not possible to freely perform a direct access to the functional blocks from external devices.
In the case where it is not possible to freely use the internal bus of the single chip microcomputer from the external devices and testing is performed on the single chip microcomputer, it is impossible to perform a direct access and testing on the functional blocks in the single chip microcomputer from the external devices. Hence, in order to perform the testing on the functional blocks, it is necessary to use an instruction execution of the central processing unit (CPU) contained in the single chip microcomputer and a time for processing steps therefor must be required. In-circuit testing is described, for example, in prior U.S. Pat. No. 4,555,783; the electrical components are tested under computer program control. Therefore, there is a problem in that the efficiency for testing on the functional blocks should become lower for a prior art single chip microcomputer than for a prior art multichip microcomputer.
Accordingly, it is a general object of the present invention to provide a data processor in which the testing efficiency on the functional blocks can be improved.
This and other objects and novel features will become apparent from the following detailed description made in connection with the accompanying drawings.